Method for manufacturing high-density indium tin oxide target, methods for preparing tin oxide powder and indium oxide powder used therefor

ABSTRACT

A method for manufacturing an indium tin oxide (ITO) target and methods for preparing indium oxide powder (In 2 O 3 ) and tin oxide powder (SnO 2 ). The method for manufacturing an ITO (indium tin oxide) target includes preparing an In 2 O 3  powder having a surface area of about 10-18 m 2 /g and an average particle diameter of between about 40 to 80 nm; preparing a SnO 2  powder having a surface area of about 8-15 m 2 /g and an average particle diameter of about 60-100 nm; molding a mixture of the In 2 O 3  powder and the SnO 2  powder; and sintering the mixture at atmospheric pressure under oxidation atmosphere. The ITO target is applicable for a high-quality, transparent electrode for a display, such as a liquid crystal display, electroluminescent display, or field emission display.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part application of U.S.patent application Ser. No. 10/320,406, entitled, “INDIUM OXIDE POWDER,METHOD FOR PREPARING THE SAME, AND METHOD FOR MANUFACTURING HIGH-DENSITYINDIUM TIN OXIDE TARGET,” and U.S. patent application Ser. No.10/320,408, entitled, “TIN OXIDE POWDER, METHOD FOR PREPARING THE SAME,AND METHOD FOR MANUFACTURING HIGH-DENSITY INDIUM TIN OXIDE TARGET,” bothof which were filed on Dec. 17, 2002 now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for manufacturing an indiumtin oxide (ITO) target and methods for preparing indium oxide powder(In₂O₃) and tin oxide powder (SnO₂). More particularly, the presentinvention relates to a method for manufacturing a high-density ITOtarget which is used in vacuum deposition of a high-quality transparentelectrode layer of a display such as a liquid crystal display (LCD),electroluminescent (EL) display, and field emission display (FED), andmethods for preparing indium oxide powder and tin oxide powder used inthe manufacture of the high-density ITO target.

2. Description of the Related Art

Due to their conductivity and transparency with respect to visiblelight, ITO films with the composition of In₂O₃ and SnO₂ in a ratio ofabout 9:1 have been widely used as a transparent electrode film for anLCD, EL, or FED. In general, such an ITO film is coated on an insulatingsubstrate such as a glass substrate by sputtering an ITO target. The ITOtarget is manufactured by molding ITO powder into a predetermined shape,for example, a rectangular parallelepiped shape, followed by sinteringat a high temperature. To form a high-quality ITO film on the substrateby sputtering, the ITO target needs to have a high sintering density. Ifa low-density ITO target is used to form an ITO film by sputtering,nodules are easily generated on the target surface, thereby lowering thequality and yield of the resulting ITO film.

For this reason, a high-density ITO target is required to form ahigh-quality, transparent ITO electrode. To form such a high-density ITOtarget, ITO particles should be of an appropriate primary particlediameter. In general, the ITO particle diameter is inverselyproportional to the target's sintering density. Therefore, the particlediameter should be reduced to increase the sintering density of thetarget. A method that is currently available for forming a high-densitytarget having an approximately theoretical density is to reduce theparticle diameter to a nano-scale. To manufacture a high-density target,it is important to adjust the ITO particle diameter to be uniform, aswell as to reduce the particle diameter, for the following reasons. If aprimary particle diameter of the ITO particles is too small, it isdifficult to grind the particles after hydroxide calcination even thoughthe driving force for sintering increases sufficiently for highersintering density due to an increased specific surface area. It is alsodifficult to obtain a large molded body due to stress caused from thegeneration of many fine pores between the particles during targetmolding. In contrast, if a primary particle diameter of the ITOparticles is too large, the fluidity and molding properties of thepowder are improved, whereas the driving force for particle sintering istoo low, so that pores between the particles become greatly enlarged,thereby increasing the energy requirement for removing the pores. Forthese reasons, to manufacture a high-density ITO target, the particlediameter should be fine and within a narrow range, and it should be easyto grind secondary particles.

A vapor phase method known for fine powder synthesis has been attractingattention as a method for nano-sized powder synthesis, but is limited tosmall-scale production of specific powder due to the difficulty oflarge-scale production. In this method, after powder synthesis, theparticle diameter is reduced by grinding. In other words, the particlediameter of secondary particles rather than primary particles, whichagglomerate to form the secondary particles, is controlled.

A liquid phase method has been used as a general method of large-scalepowder production. Among other liquid phase methods, a precipitationmethod has been especially widely used to prepare ITO powder byprecipitating metallic ions in a solution using a precipitant. In theprecipitation method, the powder's characteristics are dependent uponthe solution concentration, the reaction pH, the reaction temperature,the type of precipitant, the rate of adding a precipitant, etc.

The inventors of the present invention have discovered that theconcentrations of the indium solution and tin solution are an importantfactor affecting the characteristics of the In₂O₃ powder and SnO₂ powderprepared by precipitation. However, none of the methods of the prior arthave limited the concentration of the indium solution and tin solutionfor precipitation. As a result, until now, it has been highly difficultto control the surface area and average particle diameter of the In₂O₃powder and SnO₂ powder even when controlling the pHs of the indiumsolution and tin solution, the temperature of precipitation reaction,the type of precipitant, the rate of adding the precipitant, etc.Accordingly, until now, it has been difficult to manufacture ahigh-density ITO target using the In₂O₃ powder and SnO₂ powder preparedby those methods.

SUMMARY OF THE INVENTION

It is a feature of an embodiment of the present invention to provide amethod for manufacturing a high-density indium tin oxide (ITO) targethaving a sintering density approximate to a theoretical level.

It is another feature of an embodiment of the present invention toprovide methods for preparing indium oxide (In₂O₃) powder and tin oxide(SnO₂) powder, both of which can be used in the manufacture of thehigh-density ITO target.

In order to provide the above features, an embodiment of the presentinvention provides a method of preparing an ITO target, comprising:

preparing an In₂O₃ powder having a surface area of about 10-18 m²/g andan average particle diameter of between about 40 to 80 nm; preparing aSnO₂ powder having a surface area of about 8-15 m²/g and an averageparticle diameter of about 60-100 nm; molding a mixture of the In₂O₃powder and the SnO₂ powder; and sintering the mixture at atmosphericpressure under oxidation atmosphere. The mixture includes about 80-95%by weight of the In₂O₃ powder and about 5-20% by weight of the SnO₂powder. The ITO target has a sintering density of greater than 7.0g/cm³, more specifically a sintering density of about 7.0-7.15,approximate to a theoretical density level. The sintering temperaturefor the ITO target is from about 1,200° C. to about 1,600° C.

Another embodiment of the present invention provides a method forpreparing In₂O₃ powder, comprising: adding an alkaline precipitant to anindium solution having an indium ion concentration of about 2-5 M atroom temperature, wherein the alkaline precipitant is added to theindium solution at a rate of about 0.5 L/min - about 4 L/min, whileadjusting a pH of the indium solution to about 6-8 to form a In(OH)₃precipitate; and calcining the In(OH)₃ precipitate at a temperature ofbetween about 600° C. to about 1,100° C. to produce the In₂O₃ powder.The In₂O₃ powder preparation method may further include dissolvingmetallic indium in acid to form the indium solution. The In₂O₃ powderpreparation method may further include dissolving an indium-containingsalt in water to form the indium solution. In the present In₂O₃ powderpreparation method, the indium-containing salt may include InCl3 and/orIn(NO₃)₃. In the present In₂O₃ powder preparation method, the alkalineprecipitant may include NH4OH, NH₃ gas, NaOH, KOH, NH₄HCO₃, (NH₄)₂CO₃,and/or a mixture including at least two of the foregoing materials. TheIn₂O₃ powder preparation method may further include washing and dryingthe precipitate before calcining.

Another embodiment of the present invention provides a method forpreparing SnO₂ powder, comprising: preparing a tin solution bydissolving metallic tin in an acid, the tin solution consistingessentially of tin ions, other ions produced from the dissociation ofthe acid, molecules of the acid, and water, wherein the tin ions are ina concentration of about 0.5-2 M; allowing a tin hydroxide precipitateto precipitate from the tin solution at room temperature and aging theprecipitate in the tin solution for about 1-24 hours; separating theprecipitate from the tin solution; and calcining the separatedprecipitate at a temperature of about 400-900° C. to obtain the SnO₂powder. In the present SnO₂ powder preparation method, the acid mayinclude nitric acid and/or sulfuric acid, preferably a concentratednitric acid and/or a concentrated sulfuric acid. The structural formulaof the precipitate is Sn(OH)₂ and/or Sn(OH)₄. The SnO₂ powderpreparation method may further comprise washing and drying the separatedprecipitate before the calcining.

Another embodiment of the present invention provides another method forpreparing SnO₂ powder, comprising: preparing a tin solution bydissolving a tin-containing salt in water, the tin solution consistingessentially of tin ions, other ions produced from the dissociation ofthe salt, and water, wherein the tin ions are in a concentration ofabout 0.5-2 M; precipitating a precipitate of tin hydroxide by adding analkaline precipitant to the tin solution at room temperature at a rateof about 0.5-3 L/min and adjusting the pH to about 3-7, and separatingthe precipitate from the tin solution; and calcining the separatedprecipitate at a temperature of about 400-900° C. to obtain the SnO₂powder. In the method for preparing the SnO₂ powder in this embodimentof the present invention, the tin-containing salt may include SnF₄,SnCl₄, SnI₄, Sn(C₂H₃O₂)₂, SnCl₂, SnBr₂, SnI₂, and/or a mixture includingat least two of the foregoing materials. The alkaline precipitant mayinclude NH₄OH, NH₃ gas, NaOH, KOH, NH₄HCO₃, (NH₄)₂CO₃, and/or a mixtureincluding at least two of the foregoing materials. Preferably, the NH₄OHis 28 wt % NH₄OH. The SnO₂ powder method may further comprise washingand drying the separated precipitate before calcining the precipitate,as in the method described above.

In another embodiment of the present invention, there is provided an ITO(indium tin oxide) target having a sintering density of greater than 7.0g/cm³, more specifically a-sintering density of about 7.0-7.15,approximate to a theoretical density level. The ITO target is aresultant of sintering a mixture of an In₂O₃ powder having a surfacearea of about 10-18 m²/g and an average particle diameter of betweenabout 40 to 80 nm and a SnO₂ powder having a surface area of about 8-15m²/g and an average particle diameter of about 60-100 nm. The mixturemay include about 80-95% by weight of the In₂O₃ powder and about 5-20%by weight of the SnO₂ powder.

With the ITO target provided according to the present invention, ahigh-quality transparent electrode for a display such as a liquidcrystal display (LCD), electroluminescent display (EL), such as organiclight emitting diode (OLED), or field emission display (FED), may beeasily manufactured.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill become more apparent by describing in detail exemplary embodimentsthereof with reference to the attached drawings in which:

FIG. 1 depicts a flowchart for illustrating a method for preparingindium oxide (In₂O₃) powder according to an embodiment of the presentinvention;

FIG. 2 depicts a flowchart for illustrating first and second embodimentsof a method for preparing tin oxide (SnO₂) powder according to thepresent invention; and

FIG. 3 depicts a flowchart for illustrating an embodiment of a methodfor manufacturing an indium tin oxide (ITO) target according to thepresent invention by mixing the In₂O₃ powder prepared by the methoddepicted in FIG. 1 with the SnO₂ powder prepared by the method depictedin FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

Korean patent application No. 2002-15609, filed on Mar. 22, 2002, in theKorean Intellectual Property Office, and entitled: “TIN OXIDE POWDER,METHOD FOR PREPARING THE SAME, AND METHOD FOR MANUFACTURING HIGH-DENSITYINDIUM TIN OXIDE TARGET,” and Korean patent application No. 2002-15610,filed on Mar. 22, 2002, in the Korean Intellectual Property Office, andentitled: “INDIUM OXIDE POWDER, METHOD FOR PREPARING THE SAME, ANDMETHOD FOR MANUFACTURING HIGH-DENSITY INDIUM TIN OXIDE TARGET,” areincorporated by reference herein in their entirety.

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, in which exemplary embodimentsof the invention are illustrated. The invention may, however, beembodied in different forms and should not be construed as limited tothe embodiments set forth herein. Rather, these embodiments are providedso that this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art.

As used herein, the expressions “at least one,” “one or more,” and“and/or” are open-ended expressions that are both conjunctive anddisjunctive in operation. For example, each of the expressions “at leastone of A, B, and C,” “at least one of A, B, or C,” “one or more of A, B,and C,” “one or more of A, B, or C” and “A, B, and/or C” includes thefollowing meanings: A alone; B alone; C alone; both A and B together;both A and C together; both B and C together; and all three of A, B, andC together. Further, these expressions are open-ended, unless expresslydesignated to the contrary by their combination with the term“consisting of.” For example, the expression “at least one of A, B, andC” may also include a fourth member, whereas the expression “at leastone selected from the group consisting of A, B, and C” does not.

A method for preparing the In₂O₃ powder, a method for preparing the SnO₂powder, and a method for manufacturing an indium tin oxide (ITO) targetusing the In₂O₃ powder and the SnO₂ powder according to the presentinvention will now be described in detail.

The inventors of the present invention have discovered that fine,uniform, highly pure In₂O₃ powder suitable for a high-density ITO targetmay be prepared by systematically and accurately controlling theconcentration of an indium solution as well as the temperature ofprecipitation reaction, the pH of the indium solution, the calcinationtemperature of In₂O₃ precipitate.

In preparing fine, uniform, highly pure In₂O₃ powder, the inventors ofthe present invention have discovered that the concentration of theindium solution is an important factor. According to the mechanism ofparticle formation by a precipitation method, precipitate nuclei aregenerated in a reaction solution with the addition of a precipitant.Precipitate nuclei collide and grow into primary particles. Theseprimary particles generate nano-sized powder. In view of theprecipitation mechanism, the solution concentration affects the numberof precipitate nuclei during the precipitation and the probability ofthe nuclei colliding, and thus determines the size and shape of theparticles. In particular, in a high-concentration reaction solution,precipitate nuclei are more likely to collide so that larger particlesthan those obtained by using a low-concentration reaction solution maybe formed. Due to irregular collisions of particles, particles of avariety of shapes are precipitated. Spherical particles are favorable toincreasing the density of a sintered ITO body. In this respect, theconcentration of the indium solution is one of the most importantfactors in preparing In₂O₃ powder. When In₂O₃ powder is formed with theaddition of a precipitant to an indium solution, particle shape and sizeare determined according to the initial concentration of indium. In oneembodiment of the present invention, spherical In₂O₃ powder of aparticular size and surface area, capable of being sintered into ahigh-density ITO target, is prepared by adjusting the initialconcentration of indium ions in an indium solution.

The present invention also provides a method for manufacturing ahigh-density ITO target by limiting the average particle diameter ofSnO₂ powder to provide a maximum sintering density when mixed with theIn₂O₃ powder of a particular size and surface area prepared by thefollowing method according to the present invention.

Hereinafter, a method for preparing In₂O₃ powder according to apreferred embodiment of the present invention will be described indetail with reference to FIG. 1.

FIG. 1 depicts a flowchart for illustrating an embodiment of a methodfor preparing InO₃ powder according to the present invention. Referringto FIG. 1, as a source material for the In₂O₃ powder, metallic indium orany suitable indium-containing salt, such as InCl₃, In(NO₃)₃, etc., maybe used (Step 1). When metallic indium is used, an indium solution isobtained by dissolving the metallic indium in an acid such as a nitricacid. When an indium-containing salt is used, an indium solution isprepared by dissolving the indium-containing salt in distilled water(Step 3). The initial concentration of indium ions is controlled toabout 2-5 M. If the concentration of indium ions is less than about 2 M,precipitation reaction time may be increased, and yield may bedecreased. If the concentration of indium ions is greater than about 5M, non-uniform particles may be produced because the precipitant may notbe mixed smoothly due to thickening of the precipitate slurry duringprecipitation.

Next, an alkaline precipitant is added to the indium solution preparedas described above at room temperature to obtain In(OH)₃ precipitate(Step 5). Types of available alkaline precipitants are not limited. Forexample, NH₄OH, NH₃ gas, NaOH, KOH, NH₄HCO₃, (NH₄)₂CO₃, and/or a mixtureincluding at least two of the foregoing materials may be used as thealkaline precipitant. Preferably, the alkaline precipitant is 28 wt %NH₄OH (28% by weight of ammonia (NH₃) in water) in that it helps achieveIn₂O₃ powder of a particular and uniform particles size and sphericalshape, capable of being sintered into a high-density ITO target.

The rate of adding the precipitant is adjusted to about 0.5-4 L/min. Ifthe rate of adding the precipitant is less than about 0.5 L/min,precipitation reaction time may be increased. If the rate of adding theprecipitant is greater than about 4 L/min, the precipitant may not bemixed thoroughly, causing partial precipitation, thereby resulting innon-uniform precipitate particles. The pH of the indium solution isadjusted to about 6 to 8. If the pH of the indium solution is less thanabout 6, the precipitate particles may be very small. The pH of theindium solution greater than about 8 may have an adverse effect on theenvironment due to excess hydroxyl (OH) groups. In an implementation,the pH of the indium solution may be adjusted to an acidic pH, i.e.,below pH 7, where pH 7 is neutral (not acidic or basic). For example,the pH of the indium solution may be adjusted to an acidic pH of about 6or above and below pH 7. In an implementation, the addition of thealkaline precipitant may be carried out at room temperature. In themeaning of the present invention, the room temperature denotes thetemperature range of less than 35° C., preferably, about 10° C.˜30° C.,and more preferably, about 15° C.˜25° C., unless specified otherwise.

Subsequently, the precipitate is aged, separated using a centrifuge, andwashed (Step 7). The washed precipitate is dried in an oven (Step 9),ground, and calcined in an electric furnace (Step 11) to obtain In₂O₃powder. The calcination temperature is adjusted to between about 600 to1100° C. If the calcination temperature is lower than about 600° C., theaverage particle diameter of the In₂O₃ powder may be too small. If thecalcination temperature is higher than about 1100° C., the In₂O₃ powdermay be sintered.

With the In₂O₃ powder preparation method according to the presentinvention as described above, In₂O₃ powder having a surface area ofabout 10-18 m²/g and an average particle diameter of between about 40 to80 nm when measured by a BET method may be obtained. If a surface areaof the In₂O₃ powder measured by the BET method is less than about 10m²/g (corresponding to an average particle diameter of about 80 nm), theprimary average particle diameter may be too large to provide enoughdriving force for a high sintering density. If a surface area of theIn₂O₃ powder is larger than about 18 m²/g (corresponding to an averageparticle diameter of about 40 nm), the primary average particle diametermay be too fine to mold the In₂O₃ powder. Accordingly, it may bedifficult to achieve and obtain both a high molding density and a highsintering density.

Hereinafter, a method for preparing the SnO₂ according to the presentinvention will be described in detail.

In preparing fine, uniform, highly pure SnO₂ powder, the tin ionconcentration of the tin solution is considered to be an importantfactor for the following reason. According to the mechanism of particleformation by a precipitation method, precipitate nuclei are generated ina reaction solution with the addition of a precipitant. Precipitatenuclei collide and grow into primary particles. These primary particlesgenerate nano-sized powder. In view of the precipitation mechanism, thesolution concentration affects the number of precipitate nuclei duringthe precipitation and the probability of the nuclei colliding, and thusdetermines the size and shape of the particles. In particular, in ahigh-concentration reaction solution, precipitate nuclei are more likelyto collide so that larger particles than those obtained by using alow-concentration reaction solution may be formed. Due to irregularcollisions of particles, particles of a variety of shapes areprecipitated. Spherical particles are favorable to increase the densityof a sintered ITO body. In this respect, concentration is regarded asone of the most important factors in preparing SnO₂ powder. When SnO₂powder is formed with the addition of a precipitant to a tin solution,particle shape and size are determined according to the initialconcentration of tin. In one embodiment of the present invention,spherical SnO₂ particles of a particular size and surface area, capableof being sintered into a high-density ITO target, are prepared byadjusting the initial concentration of tin ions in a tin solution.Comparing with a conventional method in which SnO₂ synthesis is followedby particle size control using a jet mill, the method for preparing SnO₂powder according to the present invention is advantageous in that theSnO₂ powder of a particular average particle diameter and surface areafor a high-density ITO target may be directly and convenientlysynthesized.

FIG. 2 depicts a flowchart for illustrating first and second embodimentsof a method for preparing SnO₂ powder according to the presentinvention. A first embodiment of the SnO₂ powder preparation method willbe described first. Metallic tin is used as a source material (Step 1).Metallic tin is dissolved in an acid, such as a concentrated nitric acidand/or a concentrated sulfuric acid, to prepare a tin solution, fromwhich a tin hydroxide precipitate, such as a Sn(OH)₂ and/or Sn(OH)₄, isobtained (Steps 3 and 5). The tin hydroxide precipitate is allowed toprecipitate from the tin solution. SnO₂ powder of a desired size andsurface area is obtained by adjusting the concentration of tin ions inthe tin solution to about 0.5-2 M. If the concentration of the tin ionsis less than about 0.5 M, precipitation reaction efficiency may be poor.If the concentration of the tin ions is greater than about 2 M,non-uniform particles may be produced due to thickening of theprecipitate slurry during precipitation.

Next, the tin hydroxide precipitate is allowed to precipitate from thetin solution at room temperature and aged in the tin solution for about1-24 hours, preferably for about 1-12 hours, separated bycentrifugation, and washed (Step 7). Usually, it is sufficient for theageing time to be in the range of about 1-4 hours. In fact, theinventors found that there is no problem in carrying out the preparationof the SnO₂ powder even when the ageing time is shortened to as short asabout 1 hour. The washed precipitate is dried in an oven (Step 9),ground, and calcined in an electric furnace (Step 11) to obtain SnO₂powder (Step 13). The calcination temperature is adjusted to about400-900° C. If the calcination temperature is lower than about 400° C.,the average particle diameter of the SnO₂ powder may be too small. Ifthe calcination temperature is higher than about 900° C., the SnO₂powder may be sintered.

Hereinafter, a second embodiment of the method for preparing SnO₂ powderaccording to the present invention will be described with reference toFIG. 2. A tin-containing salt, instead of metallic tin, is used as asource material (Step 1). Any suitable tin-containing salt soluble ordecomposable in water, including SnF₄, SnCl₄, SnI₄, Sn(C₂H₃O₂)₂, SnCl₂,SnBr₂, SnI₂, and/or a mixture including at least two of the foregoingsalts, may be used as a material for SnO₂ powder. In the secondembodiment, an aqueous tin solution of the tin-containing salt indistilled water is used (Step 3). The initial concentration of tin ionsis adjusted to about 0.5-2 M. Next, an alkaline precipitant is added tothe aqueous tin solution at room temperature to obtain tin hydroxideprecipitate (Step 5). The tin hydroxide precipitate may include, e.g.,stannous hydroxide, Sn(OH)₂, and/or stannic hydroxide, Sn(OH)₄. The pHof the aqueous tin solution is adjusted to about 3-7 for the tinhydroxide precipitate. If the pH of the aqueous tin solution is lessthan 3, the precipitate particles may be very small. If the pH of theaqueous tin solution is greater than 7, an adverse effect on theenvironment due to excess hydroxyl (OH) groups may occur. The tinhydroxide precipitate is allowed to precipitate from the tin solution.As described above, no precipitant is necessary to obtain theprecipitate in the first embodiment of the SnO₂ preparation method,whereas an alkaline precipitant is used to obtain the precipitate in thesecond embodiment. Types of available alkaline precipitants are notlimited. For example, NH₄OH, NH₃ gas, NaOH, KOH, NH₄HCO₃, (NH₄)₂CO₃,and/or a mixture including at least two of these salts may be used asthe alkaline precipitant. Preferably, the alkaline precipitant is 28 wt% NH₄OH in that it helps achieve SnO₂ powder of a particular and uniformparticles size and spherical shape, capable of being sintered into ahigh-density ITO target. The rate of adding the precipitant is adjustedto about 0.5-3 L/min. If the rate of adding the precipitant is less thanabout 0.5 L/min, precipitation reaction time may be increased. If therate of adding the precipitant is greater than about 3 L/min, theprecipitant may not be mixed thoroughly, causing partial precipitation,thereby resulting in non-uniform precipitate particles. The followingprocesses, including aging, separation, washing (Step 7), drying (Step9), and calcination (Step 11) of the precipitant, to obtain the SnO₂powder (Step 13), are the same as those performed in the firstembodiment described above.

With the SnO₂ powder preparation method according to the first or secondembodiment of the present invention, it is possible to convenientlyprepare SnO₂ powder having a surface area of about 8-15 m₂/g and anaverage particle diameter of about 60-100 nm when measured by a BETmethod. If a surface area of the SnO₂ powder measured by the BET methodis less than about 8 m²/g (corresponding to an average particle diameterof 100 nm), the primary average particle diameter may be too. large toprovide enough driving force for a high sintering density. If a surfacearea of the SnO₂ powder is larger than about 15 m²/g (corresponding toan average particle diameter of 60 nm), the primary average particlediameter may be too fine to mold the SnO₂ powder. Accordingly, it may bedifficult to achieve and obtain both a high molding density and highsintering density.

Hereinafter, a method for manufacturing a high-density ITO target usingthe In₂O₃ powder prepared as described above by the method according tothe present invention, which has a surface area of about 10-18 m²/g andan average particle diameter of between about 40 to 80 nm when measuredby the BET method; and the SnO₂ powder prepared as described above bythe method according to the present invention, which has a surface areaof about 8-15 m²/g and an average particle diameter of about 60-100 nmwhen measured by the BET method, will be described.

FIG. 2 depicts a flowchart for illustrating a method for preparing ahigh-density ITO target by mixing the In₂O₃ powder with the SnO₂ powderprepared by the methods according to the present invention. Referring toFIG. 2, about 80-95% by weight of the In₂O₃ powder prepared according tothe present invention and about 5-20% by weight of SnO₂ powder preparedaccording to the present invention are mixed. The In₂O₃ powder has asurface area of about 5-18 m²/g, preferably 10-18 m²/g, when measured bythe BET method. The SnO₂ powder has a surface area of between about 4 to15 m²/g, preferably between about 8 to 15 m²/g, when measured by the BETmethod. The In₂O₃ and the SnO₂ are mixed by, for example, ball milling(Step 15). The resulting powder mixture is dried and molded into arectangular parallelepiped target (Step 17). The molded product isthermally treated for sintering at between about 1,200 to 1,600° C. in asintering furnace at atmospheric pressure under oxidation atmosphere toobtain an ITO target (Step 19). The characteristics of the final ITOtarget are evaluated by measuring, for example, the sintering density.If the sintering temperature is lower than about 1,200° C., it may bedifficult to completely solidify the two oxides during the sintering,and the energy may be insufficient for a high sintering density. If thesintering temperature is above about 1,600° C., which is high enough forphase change and sintering of the oxides, the yield of the ITO targetmay decrease with increasing sintering duration because In₂O₃ and Sn₂are volatile at high temperatures.

As described above, the method of forming a high-density ITO targetaccording to the present invention may provide sintered ITO bodies withdensities of about 7.0 to about 7.15 g/cm³, e.g., 7.08 to 7.14 g/cm³,which may be considerably higher than the densities of the sintered ITObodies produced using conventional methods. Moreover, it is surprisingthat such a high-density ITO target can be obtained through a sinteringprocess operating at atmospheric pressure.

The methods for preparing In₂O₃ powder and SnO₂ powder, and the methodfor manufacturing an ITO target according to the present invention willbe described in greater detail with reference to the following examples.

The following examples are for illustrative purposes and are notintended to limit the scope of the invention.

Synthesis of SnO₂ Powder

A method for synthesizing SnO₂ powder to be mixed with In₂O₃ powder andsintered to form ITO targets in the following examples 1 through 6 andcomparative examples 1-7 is described herein. SnCl₄ was dissolved in 5 Lof water to obtain a tin ion solution containing tin ions in aconcentration of 1.0 M. 28 wt % NH₄OH precipitant was added to thesolution at a rate of 1 L/min to obtain tin hydroxide precipitate. Thetin hydroxide precipitate was aged for 9-12 hours, separated using acentrifuge, and washed with distilled water. The washed precipitate wasdried at 100° C. in an oven, and the dried powder was ground. The groundpowder was calcined in an electric furnace at 700° C. for 2 hours. Theresulting SnO₂ powder had a surface area of 10 m²/g when measured by theBET method.

EXAMPLE 1

A predetermined amount of In(NO₃)₃, equivalent to a final indium ionconcentration of 2.5 M, was dissolved in 5 L of distilled water. Aprecipitate was obtained by adding 28 wt % NH₄OH as a precipitant to thesolution at a rate of 2 L/min at room temperature. The pH of thesolution was adjusted to 8. The resulting precipitate was aged for 9-12hours, separated using a centrifuge, and washed. The washed precipitatewas dried at 100° C. in an oven, and the dried powder was ground by ballmilling. The ground powder was calcined in an electric furnace at 700°C. for 2 hours. The resulting In₂O₃ powder had a surface area of 18 m²/gwhen measured by the BET method.

The In₂O₃ powder prepared as described above and SnO₂ powder having asurface area of 10 m²/g when measured by the BET method were mixed in aweight ratio of 90:10. The powder mixture was molded into apredetermined shape using a mold and sintered at atmospheric pressureunder oxidation atmosphere. The resulting ITO target of a 20-cm width,15-cm length, and 1-cm height had a sintering density of 7.13 g/cm³.

EXAMPLE 2

In Example 2, 1436 g of metallic indium was completely dissolved in 5 L60 wt %-nitric acid to obtain a 2.5 M In(NO₃)₃ solution. A precipitatewas obtained by adding 28 wt % NH₄OH as a precipitant to the solution ata rate of 2 L/min at room temperature. The pH of the solution wasadjusted to 8. The resulting precipitate was aged for 9-12 hours,separated using a centrifuge, and washed. The washed precipitate wasdried at 100° C. in an oven, and the dried powder was ground by ballmilling. The ground powder was calcined in an electric furnace at 800°C. for 2 hours. The resulting In₂O₃ powder had a surface area of 17 m²/gwhen measured by the BET method.

The In₂O₃ powder prepared as described above and SnO₂ powder having asurface area of 10 m²/g when measured by the BET method were mixed in aweight ratio of 90:10. The powder mixture was molded into apredetermined shape and sintered at atmospheric pressure under oxidationatmosphere. The resulting ITO target of a 20-cm width, 15-cm length, and1-cm height had a sintering density of 7.14 g/cm³.

EXAMPLE 3

A predetermined amount of In(NO₃)₃, equivalent to a final indium ionconcentration of 2.5 M, was dissolved in 5 L of distilled water. Aprecipitate was obtained by adding 28 wt % NH₄OH as a precipitant to thesolution at a rate of 0.5 L/min at room temperature. The pH of thesolution was adjusted to 8. The resulting precipitate was aged for 9-12hours, separated using a centrifuge, and washed. The washed precipitatewas dried at 100° C. in an oven, and the dried powder was ground by ballmilling. The ground powder was calcined in an electric furnace at 800°C. for 2 hours. The resulting In₂O₃ powder had a surface area of 16 m²/gwhen measured by the BET method.

The In₂O₃ powder prepared as described above and SnO₂ powder having asurface area of 10 m²/g when measured by the BET method were mixed in aweight ratio of 90:10. The powder mixture was molded into apredetermined shape using a mold and sintered at atmospheric pressureunder oxidation atmosphere. The resulting ITO target of a 20-cm width,15-cm length, and 1-cm height had a sintering density of 7.08g/cm^(3l .)

EXAMPLE 4

A predetermined amount of In(NO₃)₃ was dissolved in 5 L of distilledwater to obtain an indium solution having an indium ion concentration of3.0 M. A precipitate was obtained by adding 28 wt % NH₄OH as aprecipitant to the solution at a rate of 2 L/min at room temperature.The pH of the solution was adjusted to 7. The resulting precipitate wasstirred, aged for 9-12 hours, separated using a centrifuge, and washed.The washed precipitate was dried at 100° C. in an oven, and the driedpowder was ground by ball milling. The ground powder was calcined in anelectric furnace at 800° C. for 2 hours. The resulting In₂O₃ powder hada surface area of 14 m²/g when measured by the BET method.

The In₂O₃ powder prepared as described above and SnO₂ powder having asurface area of 10 m²/g when measured by the BET method were mixed in aweight ratio of 90:10. The powder mixture was molded into apredetermined shape using a mold and sintered at atmospheric pressureunder oxidation atmosphere. The resulting ITO target of a 20-cm width,15-cm length, and 1-cm height had a sintering density of 7.10 g/cm³.

EXAMPLE 5

A predetermined amount of In(NO₃)₃ was dissolved in distilled water toobtain an indium solution having an indium ion concentration of 2.5 Mwas dissolved in 5 L of distilled water. A precipitate was obtained byadding 28 wt % NH₄OH as a precipitant to the solution at a rate of 2L/min at room temperature. The pH of the solution was adjusted to 7. Theresulting precipitate was stirred, aged for 9-12 hours, separated usinga centrifuge, and washed. The washed precipitate was dried at 100° C. inan oven, and the dried powder was ground by ball milling. The groundpowder was calcined in an electric furnace at 850° C. for 2 hours. Theresulting In₂O₃ powder had a surface area of 11 m²/g when measured bythe BET method.

The In₂O₃ powder prepared as described above and SnO₂ powder having asurface area of 10 m²/g when measured by the BET method were mixed in aweight ratio of 90:10. The powder mixture was molded into apredetermined shape using a mold and sintered at atmospheric pressureunder oxidation atmosphere. The resulting ITO target of a 20-cm width,15-cm length, and 1-cm height had a sintering density of 7.13 g/cm³.

EXAMPLE 6

A predetermined amount of In(NO₃)₃ was dissolved in 5 L of distilledwater to obtain an indium solution having an indium ion concentration of2.5 M. A precipitate was obtained by adding 28 wt % NH₄OH as aprecipitant to the solution at a rate of 1 L/min at room temperature.The pH of the solution was adjusted to 7. The resulting precipitate wasstirred, aged for 9-12 hours, separated using a centrifuge, and washed.The washed precipitate was dried at 100° C. in an oven, and the driedpowder was ground by ball milling. The ground powder was calcined in anelectric furnace at 850° C. for 2 hours. The resulting In₂O₃ powder hada surface area of 12 m²/g when measured by the BET method.

The In₂O₃ powder prepared as described above and SnO₂ powder having asurface area of 10 m²/g when measured by the BET method were mixed in aweight ratio of 90:10. The powder mixture was molded into apredetermined shape using a mold and sintered at atmospheric pressureunder oxidation atmosphere. The resulting ITO target of a 20-cm width,15-cm length, and 1-cm height had a sintering density of 7.12 g/cm³.

COMPARATIVE EXAMPLE 1

A predetermined amount of In(NO₃)₃ was dissolved in 5 L of distilledwater to obtain an indium solution having an indium ion concentration of1 M.

A precipitate was obtained by adding 28 wt % NH₄OH as a precipitant tothe solution at a rate of 2 L/min at room temperature. The pH of thesolution was adjusted to 8. The resulting precipitate was stirred, agedfor 9-12 hours, separated using a centrifuge, and washed. The washedprecipitate was dried at 100° C. in an oven, and the dried powder wasground by ball milling. The ground powder was calcined in an electricfurnace at 700° C. for 2 hours. The resulting In₂O₃ powder had a surfacearea of 25 m²/g when measured by the BET method.

The In₂O₃ powder prepared as described above and SnO₂ powder having asurface area of 10 m²/g when measured by the BET method were mixed in aweight ratio of 90:10. The powder mixture was molded into apredetermined shape using a mold and sintered at atmospheric pressureunder oxidation atmosphere. The resulting ITO target had a sinteringdensity of 6.91 g/cm³.

COMPARATIVE EXAMPLE 2

A predetermined amount of In(NO₃)₃ was dissolved in 5 L of distilledwater to obtain an indium solution having an indium ion concentration of2.5 M. A precipitate was obtained by adding 28 wt % NH₄OH as aprecipitant to the solution at a rate of 0.05 L/min at room temperatureto obtain a precipitate. The pH of the solution was adjusted to 8. Theresulting precipitate was stirred, aged for 9-12 hours, separated usinga centrifuge, and washed. The washed precipitate was dried at 100° C. inan oven, and the dried powder was ground by ball milling. The groundpowder was calcined in an electric furnace at 700° C. for 2 hours. Theresulting In₂O₃ powder had a surface area of 30 m²/g when measured bythe BET method.

The In₂O₃ powder prepared as described above and SnO₂ powder having asurface area of 10 m²/g when measured by the BET method were mixed in aweight ratio of 90:10. The powder mixture was molded into apredetermined shape using a mold and sintered at atmospheric pressureunder oxidation atmosphere. The resulting ITO target had a sinteringdensity of 6.30 g/cm³.

COMPARATIVE EXAMPLE 3

A predetermined amount of In(NO₃)₃ was dissolved in 5 L of distilledwater to obtain an indium solution having an indium ion concentration of2.5 M. A precipitate was obtained by adding 28 wt % NH₄OH as aprecipitant to the solution at a rate of 2 L/min at room temperature.The pH of the solution was adjusted to 4. The resulting precipitate wasstirred, aged for 9-12 hours, separated using a centrifuge, and washed.The washed precipitate was dried at 100° C. in an oven, and the driedpowder was ground by ball milling. The ground powder was calcined in anelectric furnace at 700° C. for 2 hours. The resulting In₂O₃ powder hada surface area of 23 m²/g when measured by the BET method.

The In₂O₃ powder prepared as described above and SnO₂ powder having asurface area of 10 m²/g when measured by the BET method were mixed in aweight ratio of 90:10. The powder mixture was molded into apredetermined shape using a mold and sintered at atmospheric pressureunder oxidation atmosphere. The resulting ITO target had a sinteringdensity of 6.60 g/cm³.

COMPARATIVE EXAMPLE 4

A predetermined amount of In(NO₃)₃ was dissolved in 5 L of distilledwater to obtain an indium solution having an indium ion concentration of2.5 M. A precipitate was obtained by adding 28 wt % NH₄OH as aprecipitant to the solution at a rate of 2 L/min at room temperature toobtain a precipitate. The pH of the solution was adjusted to 8. Theresulting precipitate was stirred, aged for 9-12 hours, separated usinga centrifuge, and washed. The washed precipitate was dried at 100° C. inan oven, and the dried powder was ground by ball milling. The groundpowder was calcined in an electric furnace at 500° C. for 2-hours. Theresulting In₂O₃ powder had a surface area of 32 m²/g when measured bythe BET method.

The In₂O₃ powder prepared as described above and SnO₂ powder having asurface area of 10 m²/g when measured by the BET method were mixed in aweight ratio of 90:10. The powder mixture was molded into apredetermined shape using a mold and sintered at atmospheric pressureunder oxidation atmosphere. The resulting ITO target had a sinteringdensity of 6.48 g/cm³.

COMPARATIVE EXAMPLE 5

A predetermined amount of In(NO₃)₃ was dissolved in 5 L of distilledwater to obtain an indium solution having an indium ion concentration of5.5 M. A precipitate was obtained by adding 28 wt % NH₄OH as aprecipitant to the solution at a rate of 2 L/min at room temperature toobtain a precipitate. The pH of the solution was adjusted to 8. Theviscosity of the slurry was high due to the high-concentration reactionsolution. The resulting precipitate was stirred, aged for 9-12 hours,separated using a centrifuge, and washed. The washed precipitate wasdried at 100° C. in an oven, and the dried powder was ground by ballmilling. The ground powder was calcined in an electric furnace at 800°C. for 2 hours. The resulting In₂O₃ powder had a surface area of 4.5m²/g when measured by the BET method.

The In₂O₃ powder prepared as described above and SnO₂ powder having asurface area of 10 m²/g when measured by the BET method were mixed in aweight ratio of 90:10. The powder mixture was molded into apredetermined shape using a mold and sintered at atmospheric pressureunder oxidation atmosphere. The resulting ITO target had a sinteringdensity of 6.18 g/cm³.

COMPARATIVE EXAMPLE 6

A predetermined amount of In(NO₃)₃ was dissolved in 5 L of distilledwater to obtain an indium solution having an indium ion concentration of2.5 M. A precipitate was obtained by adding 28 wt % NH₄OH as aprecipitant to the solution at a rate of 2 L/min at room temperature toobtain a precipitate. The pH of the solution was adjusted to 8. Theresulting precipitate was stirred, aged for 9-12 hours, separated usinga centrifuge, and washed. The washed precipitate was dried at 100° C. inan oven, and the dried powder was ground by ball milling. The groundpowder was calcined in an electric furnace at 1200° C. for 2 hours.Observation using a scanning electron microscope (SEM), after thecalcination, indicated that the particles had grown significantly. Theresulting In₂O₃ powder had a surface area of 4.3 m²/g when measured bythe BET method.

The In₂O₃ powder prepared as described above and SnO₂ powder having asurface area of 10 m²/g when measured by the BET method were mixed in aweight ratio of 90:10. The powder mixture was molded into apredetermined shape using a mold and sintered. at atmospheric pressureunder oxidation atmosphere. The resulting ITO target had a sinteringdensity of 6.51 g/cm³.

COMPARATIVE EXAMPLE 7

A predetermined amount of In(NO₃)₃ was dissolved in 5 L of distilledwater to obtain an indium solution having an indium ion concentration of3.0 M. A precipitate was obtained by adding 28 wt % NH₄OH as aprecipitant to the solution at a rate of 2 L/min at room temperature toobtain a precipitate. The pH of the solution was adjusted to 10. Theresulting precipitate was stirred, aged for 9-12 hours, separated usinga centrifuge, and washed. There was a strong ammonia smell during thewash. The washed precipitate was dried at 100° C. in an oven, and thedried powder was ground by ball milling. The ground powder was calcinedin an electric furnace at 800° C. for 2 hours. Observation using ascanning electron microscope (SEM), after the calcination, indicatedthat the particles had grown significantly. The resulting In₂O₃ powderhad a surface area of 31 m²/g when measured by the BET method.

The In₂O₃ powder prepared as described above and SnO₂ powder having asurface area of 10 m²/g when measured by the BET method were mixed in aweight ratio of 90:10. The powder mixture was molded into apredetermined shape using a mold and sintered at atmospheric pressureunder oxidation atmosphere. The resulting ITO target had a sinteringdensity of 6.67 g/cm³.

The main In₂O₃ powder preparation conditions and the sintering densityof each of the ITO targets in examples 1 through 6 and comparativeexamples 1 through 7 are shown in Table 1.

TABLE 1 Sintering Rate of Surface Particle Surface Particle DensityIndium Precipitant Calcination Area of Diameter Area of Diameter of ITOConcentration Addition Reaction Temperature In₂O₃ of In₂O₃ SnO₂ of SnO₂target Example (M) (L/min) pH (° C.) (m²/g) (nm) (m²/g) (nm) (g/cm³)Example 1 2.5 2 8 700 18 46 10 86 7.13 Example 2 2.5 2 8 800 17 49 10 867.14 Example 3 2.5 0.5 8 800 16 52 10 86 7.08 Example 4 3.0 2 7 800 1460 10 86 7.10 Example 5 2.5 2 7 850 11 76 10 86 7.13 Example 6 2.5 1 7850 12 70 10 86 7.12 Comparative 1.0 2 8 700 25 34 10 86 6.91 Example 1Comparative 2.5 0.05 8 700 30 28 10 86 6.30 Example 2 Comparative 2.5 24 700 23 36 10 86 6.60 Example 3 Comparative 2.5 2 8 500 32 26 10 866.48 Example 4 Comparative 5.5 2 8 800 4.5 187 10 86 6.18 Example 5Comparative 2.5 2 8 1,200 4.3 195 10 86 6.51 Example 6 Comparative 3.0 210 800 31 27 10 86 6.67 Example 7

According to the present invention, In₂O₃ powder may be prepared as inexamples 1 through 6 by adjusting the concentration of the indiumsolution as well as the rate of adding the precipitant, the pH of theindium solution, and the calcination temperature and sintering themixture. As is apparent from Table 1, by mixing SnO₂ powder with theIn₂O₃ powder prepared according to the present invention, a high-densityITO target of above about 7.0 g/cm³ may be manufactured. Especially, inthe case of examples 1, 2, 5, and 6, a very high sintering density,approximate to a theoretical density of 7.15 g/cm³, may be obtained forthe ITO targets.

According to a preparation method of the present invention, it ispossible to conveniently manufacture In₂O₃ powder having a uniformprimary average particle diameter of 40-80 nm, which may be furtherground into secondary particles of a size (D50 or D90) less than 1 μm.Through sintering after mixing SnO₂ powder of a uniform average particlediameter with the In₂O₃ powder prepared by the method according to thepresent invention, a high-density ITO target may be manufactured. Thehigh-density ITO target according to the present invention is applicablefor a high-quality, transparent electrode film for an LCD, EL, FED, etc.by sputtering in a vacuum.

Synthesis of In₂O₃ Powder

A method for synthesizing In₂O₃ powder to be mixed with SnO₂ powder andsintered to form ITO targets in the following examples 7 through 9 andcomparative examples 8 and 9 is described herein. A predetermined amountof In(NO₃)₃, equivalent to a final indium ion concentration of 2.5 M,was dissolved in 5 L of distilled water. A precipitate was obtained byadding 28 wt % NH₄OH as a precipitant to the solution at a rate of 2L/min at room temperature. For this precipitation reaction, the pH ofthe solution was adjusted to 8. The resulting precipitate was aged for9-12 hours, separated using a centrifuge, and washed. The washedprecipitate was dried at 100° C. in an oven, and the dried powder wasground. The ground powder was calcined in an electric furnace at 700° C.for 2 hours. The resulting In₂O₃ powder had a surface area of 18 m²/gwhen measured by the BET method.

EXAMPLE 7

In Example 1, 300 g metallic tin was placed in a 5-L beaker. Themetallic tin was dissolved by adding 2.5L 60 wt % nitric acid into thebeaker, while stirring, at room temperature. The resulting mixture had atin ion concentration of 1.0 M. The tin hydroxide precipitate was agedfor 9-12 hours, separated using a centrifuge, and washed with distilledwater. The precipitate was dried at 100° C. in an oven, ground, andcalcined in an electric furnace at 600° C. for 2 hours to produce SnO₂powder. The resulting SnO₂ powder had a surface area of 14 m²/g whenmeasured by the BET method.

In₂O₃ powder having a surface area of 18 m²/g when measured by the BETmethod and the SnO₂ powder prepared as described above were mixed in aweight ratio of 90:10. The powder mixture was molded using a rectangularparallelepiped mold and sintered at 1,500° C. at atmospheric pressureunder oxidation atmosphere. The resulting ITO target of a 20-cm width,15-cm length, and 1-cm height had a sintering density of 7.13 g/cm³.

EXAMPLE 8

A predetermined amount of SnCl₄, equivalent to a final tin ionconcentration of 1.0 M, was dissolved in 5 L of distilled water. Aprecipitate was obtained by adding 28 wt % NH₄OH as a precipitant to thesolution at a rate of 1 L/min at room temperature. The pH of thesolution was adjusted to 7. The resulting precipitate was aged for 9-12hours, separated using a centrifuge, and washed. The washed precipitatewas dried at 100° C. in an oven, and the dried powder was ground. Theground powder was calcined in an electric furnace at 700° C. for 2hours. The resulting SnO₂ powder had a surface area of 12 m²/g whenmeasured by the BET method.

In₂O₃ powder having a surface area of 18 m²/g when measured by the BETmethod and the SnO₂ powder prepared as described above were mixed in aweight ratio of 90:10. The powder mixture was molded using a rectangularparallelepiped mold and sintered at 1,500° C. at atmospheric pressureunder oxidation atmosphere. The resulting ITO target of a 20-cm width,15-cm length, and 1-cm height had a sintering density of 7.14 g/cm³.

EXAMPLE 9

A predetermined amount of SnCl₄, equivalent to a final tin ionconcentration of 1.5 M, was dissolved in 5 L of distilled water. Aprecipitate was obtained by adding 28 wt % NH₄OH as a precipitant to thesolution at a rate of 2 L/min at room temperature. The pH of thesolution was adjusted to 7. The resulting precipitate was aged for 9-12hours, separated using a centrifuge, and washed. The washed precipitatewas dried at 100° C. in an oven, and the dried powder was ground using ahammer mill. The ground powder-was calcined in an electric furnace at600° C. for 2 hours. The resulting SnO₂ powder had a surface area of 13m²/g when measured by the BET method.

In₂O₃ powder having a surface area of 18 m²/g when measured by the BETmethod and the SnO₂ powder prepared as described above were mixed in aweight ratio of 90:10. The powder mixture was molded using a rectangularparallelepiped mold and sintered at 1,550° C. at atmospheric pressureunder oxidation atmosphere. The resulting ITO target of a 20-cm width,15-cm length, and 1-cm height had a sintering density of 7.12 g/cm³.

COMPARATIVE EXAMPLE 8

A predetermined amount of SnCl₄, equivalent to a final tin ionconcentration of 0.3 M, was dissolved in 5 L of distilled water. Aprecipitate was obtained by adding 28 wt % NH₄OH as a precipitant to thesolution at a rate of 1 L/min at room temperature. The pH of thesolution was adjusted to 7. The resulting precipitate was aged for 9-12hours, separated using a centrifuge, and washed. The washed precipitatewas dried at 100° C. in an oven, and the dried powder was ground using ahammer mill. The ground powder was calcined in an electric furnace at600° C. for 2 hours. The resulting SnO₂ powder had a surface area of 16m²/g when measured by the BET method.

In₂O₃ powder having a surface area of 18 m²/g when measured by the BETmethod and the SnO₂ powder prepared as described above were mixed in aweight ratio of 90:10. The powder mixture was molded using a rectangularparallelepiped mold and sintered at 1,550° C. at atmospheric pressureunder oxidation atmosphere. The resulting ITO target of a 20-cm width,15-cm length, and 1-cm height had a sintering density of 6.58 g/cm³.

COMPARATIVE EXAMPLE 9

A predetermined amount of SnCl₄, equivalent to a final tin ionconcentration of 3.0 M, was dissolved in 5 L of distilled water. Aprecipitate was obtained by adding 28 wt % NH₄OH as a precipitant to thesolution at a rate of 1 L/min at room temperature. The pH of thesolution was adjusted to 7. The resulting precipitate was aged for 9-12hours, separated using a centrifuge, and washed. The washed precipitatewas dried at 100° C. in an oven, and the dried powder was ground using ahammer mill. The ground powder was calcined in an electric furnace at600° C. for 2 hours. The resulting SnO₂ powder had a surface area of 3m²/g when measured by the BET method.

In₂O₃ powder having a surface area of 18 m²/g when measured by the BETmethod and the SnO₂ powder prepared as described above were mixed in aweight ratio of 90:10. The powder mixture was molded using a rectangularparallelepiped mold and sintered at 1,550° C. at atmospheric pressureunder oxidation atmosphere. The resulting ITO target of a 20-cm width,15-cm length, and 1-cm height had a sintering density of 6.35 g/cm³.

The main SnO₂ powder preparation conditions and the sintering density ofeach of the ITO targets in examples 7 through 9 and comparative examples8 and 9 are shown in Table 2.

TABLE 2 Rate of Surface Surface Particle Sintering Tin PrecipitantCalcination Area of Area of Diameter Density of concentration AdditionReaction Temperature In₂O₃ SnO₂ of SnO₂ ITO target Example (M) (L/min)pH (° C.) (m²/g) (m²/g) (nm) (g/cm³) Example 7 1.0 — — 600 18 14 62 7.13Example 8 1.0 1 7 700 18 12 72 7.14 Example 9 1.5 2 7 600 18 13 66 7.12Comparative 0.3 1 7 600 18 16 54 6.58 Example 8 Comparative 3.0 1 7 60018 3 287 6.35 Example 9

According to the present invention, SnO₂ powder is prepared by adjustingthe concentration of tin ions as well as the rate of adding theprecipitant, the pH of the tin solution, and the calcinationtemperature, and sintering the mixture. As is apparent from Table 2, bymixing In₂O₃ powder with the SnO₂ powder prepared according to thepresent invention, a high-density ITO target of 7.12-7.14 g/cm³, whichapproximates to a theoretical density of 7.15 g/cm³, is obtained.

According to the SnO₂ powder preparation method of the presentinvention, it is possible to conveniently manufacture SnO₂ powder havinga uniform primary average particle diameter of 60-100 nm, which may thenbe further ground into secondary particles of a size (D50 or D90) lessthan 10 μm. Through sintering after mixing In₂O₃ powder of a uniformaverage particle diameter with the SnO₂ powder prepared by the methodaccording to the present invention, a high-density ITO target may bemanufactured. The high-density ITO target according to the presentinvention is applicable in forming a high-quality, transparent electrodefilm for a LCD, EL, FED, etc. by sputtering in a vacuum.

While this invention has been particularly shown and described withreference to exemplary embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention as defined by the appended claims.

1. A method of preparing an ITO (indium tin oxide) target, comprising:preparing an In₂O₃ powder having a surface area of about 10-18 m²/g andan average particle diameter of between about 40 to 80 nm; preparing aSnO₂ powder having a surface area of about 8-15 m²/g and an averageparticle diameter of about 60-100 nm; molding a mixture of the In₂O₃powder and the SnO₂ powder; and sintering the mixture at atmosphericpressure under oxidizing atmosphere.
 2. The method as claimed in claim1, wherein the mixture includes about 80-95% by weight of the In₂O₃powder and about 5-20% by weight of the SnO₂ powder.
 3. The method asclaimed in claim 1, wherein the ITO target has a sintering density ofgreater than 7.0 g/cm³.
 4. The method as claimed in claim 1, whereinsintering the mixture is performed at a temperature of about 1,200° C.to about 1,600° C.
 5. The method as claimed in claim 1, whereinpreparing the In₂O₃ powder includes: adding an alkaline precipitant toan indium solution having an indium ion concentration of about 2-5 M atroom temperature, wherein the alkaline precipitant is added to theindium solution at a rate of about 0.5 L/min - about 4 L/min, whileadjusting a pH of the indium solution to about 6-8 to form a In(OH)₃precipitate; and calcining the In(OH)₃ precipitate at a temperature ofbetween about 600° C. to about 1,100° C.
 6. The method as claimed inclaim 5, further comprising dissolving metallic indium in acid to formthe indium solution.
 7. The method as claimed in claim 5, furthercomprising dissolving an indium-containing salt in water to form theindium solution.
 8. The method as claimed in claim 7, wherein theindium-containing salt includes InCl₃ and/or In(NO₃)₃.
 9. The method asclaimed in claim 5, wherein the alkaline precipitant includes NH₄OH, NH₃gas, NaOH, KOH, NH₄HCO₃, (NH₄)₂CO₃ or a mixture including at least twoof the foregoing materials.
 10. The method as claimed in claim 9,wherein the NH₄OH is 28 wt % NH₄OH.
 11. The method as claimed in claim5, further comprising washing and drying the precipitate beforecalcining.
 12. The method as claimed in claim 1, wherein preparing theSnO₂ powder includes: preparing a tin solution by dissolving metallictin in an acid, the tin solution consisting essentially of tin ions,other ions produced from the dissociation of the acid, molecules of theacid, and water, wherein the tin ions are in a concentration of about0.5-2 M; allowing a tin hydroxide precipitate to precipitate from thetin solution at room temperature and aging the precipitate in the tinsolution for about 1-24 hours; separating the precipitate from the tinsolution; and calcining the separated precipitate at a temperature ofabout 400-900° C. to obtain the SnO₂ powder.
 13. The method as claimedin claim 12, wherein the acid includes nitric acid and/or sulfuric acid.14. The method as claimed in claim 12, wherein the structural formula ofthe precipitate is Sn(OH)₂ and/or Sn(OH)₄.
 15. The method as claimed inclaim 12, further comprising washing and drying the separatedprecipitate before the calcining.
 16. The method as claimed in claim 1,wherein preparing the SnO₂ powder includes: preparing a tin solution bydissolving a tin-containing salt in water, the tin solution consistingessentially of tin ions, other ions produced from the dissociation ofthe salt, and water, wherein the tin ions are in a concentration ofabout 0.5-2 M; precipitating a precipitate of tin hydroxide by adding analkaline precipitant to the tin solution at room temperature at a rateof about 0.5-3 L/min and adjusting the pH to about 3-7, and separatingthe precipitate from the tin solution; and calcining the separatedprecipitate at a temperature of about 400-900° C. to obtain the SnO₂powder.
 17. The method as claimed in claim 16, wherein thetin-containing salt includes SnF₄, SnCl₄, SnI₄, Sn(C₂H₃O₂)₂, SnCl₂,SnBr₂, SnI₂, or a mixture including at least two of the foregoingmaterials.
 18. The method as claimed in claim 16, wherein the alkalineprecipitant includes NH₄OH, NH₃ gas, NaOH, KOH, NH₄HCO₃, (NH₄)₂CO₃, or amixture including at least two of the foregoing materials.
 19. Themethod as claimed in claim 18, wherein the NH₄OH is 28 wt % NH₄OH. 20.The method as claimed in claim 16, further comprising washing and dryingthe separated precipitate before calcining the precipitate.
 21. A methodof preparing an ITO (indium tin oxide) target, comprising: preparing anIn₂O₃ powder having a surface area of about 5-18 m²/g and an averageparticle diameter of between about 40 to 160 nm; preparing a SnO₂ powderhaving a surface area of about 4-15 m²/g and an average particlediameter of about 50-200 nm; molding a mixture of the In₂O₃ powder andthe SnO₂ powder; and sintering the mixture at atmospheric pressure underoxidizing atmosphere.